Abstract:

A copolymer of an alkali-soluble (α-trifluoromethyl)-acrylate and a
norbornene derivative is useful as an additive to a resist composition.
When processed by immersion lithography, the resist composition exhibits
excellent water repellency and water slip and forms a pattern with few
development defects.

Claims:

1. A resist composition comprising (A) a polymer P1 comprising repeat
units of the following general formulae (1a) and (2a), (B) a polymer
having a structure containing one or both of a lactone ring and a
hydroxyl group, and/or a structure derived from maleic anhydride, which
polymer becomes soluble in an alkaline developer under the action of an
acid, (C) a compound capable of generating an acid upon exposure to
high-energy radiation, and (D) an organic solvent, ##STR00088## wherein
R1a and R1b are hydrogen or straight, branched or cyclic
C1-C10 alkyl, R1a and R1b may bond together to form a
non-aromatic ring with the carbon atom to which they are attached,
R2 is hydrogen, methyl or trifluoromethyl, R3 is hydrogen or an
acid labile group, a1 and b1 are numbers satisfying 0<a1<1,
0<b1<1, and 0<a1+b1.ltoreq.1.

2. A resist composition comprising (A) a polymer P1' comprising repeat
units of the following general formulae (1a), (1b) and (2a), (B) a
polymer having a structure containing one or both of a lactone ring and a
hydroxyl group, and/or a structure derived from maleic anhydride, which
polymer becomes soluble in an alkaline developer under the action of an
acid, (C) a compound capable of generating an acid upon exposure to
high-energy radiation, and (D) an organic solvent, ##STR00089## wherein
R1a and R1b are hydrogen or straight, branched or cyclic
C1-C10 alkyl, R1a and R1b may bond together to form a
non-aromatic ring with the carbon atom to which they are attached,
R2 is hydrogen, methyl or trifluoromethyl, R3 is hydrogen or an
acid labile group, R4a to R4c are hydrogen or straight,
branched or cyclic C1-C10 alkyl, and a1, a2 and b1 are numbers
satisfying 0<a1<1, 0<a2<1, 0<b1<1, and
0<a1+a2+b1.ltoreq.1.

3. A resist composition comprising (A) a polymer P1'' comprising repeat
units of the following general formulae (1a), (1b), (2a) and (2b), (B) a
polymer having a structure containing one or both of a lactone ring and a
hydroxyl group, and/or a structure derived from maleic anhydride, which
polymer becomes soluble in an alkaline developer under the action of an
acid, (C) a compound capable of generating an acid upon exposure to
high-energy radiation, and (D) an organic solvent, ##STR00090## wherein
R1a and R1b are hydrogen or straight, branched or cyclic
C1-C10 alkyl, R1a and R1b may bond together to form a
non-aromatic ring with the carbon atom to which they are attached,
R2 is hydrogen, methyl or trifluoromethyl, R3 is hydrogen or an
acid labile group, R4a to R4c are hydrogen or straight,
branched or cyclic C1-C10 alkyl, R5 is straight, branched
or cyclic C1-C10 alkyl, and a1, a2, b1 and b2 are numbers
satisfying 0<a1<1, 0.ltoreq.a2<1, 0.ltoreq.b1<1,
0<b2<1, and 0<a1+a2+b1+b2.ltoreq.1.

4. A resist composition comprising (A) a polymer P2 corresponding to a
polymer P1-H comprising repeat units of the following general formulae
(1a) and (2a') wherein some or all of hydroxyl groups in formulae (1a)
and (2a') are protected with protective groups, (B) a polymer having a
structure containing one or both of a lactone ring and a hydroxyl group,
and/or a structure derived from maleic anhydride, which polymer becomes
soluble in an alkaline developer under the action of an acid, (C) a
compound capable of generating an acid upon exposure to high-energy
radiation, and (D) an organic solvent, ##STR00091## wherein R1a and
R1b are hydrogen or straight, branched or cyclic C1-C10
alkyl, R1a and R1b may bond together to form a non-aromatic
ring with the carbon atom to which they are attached, R2 is
hydrogen, methyl or trifluoromethyl, and a1 and b1 are numbers satisfying
0<a1<1, 0<b1<1, and 0<a1+b1.ltoreq.1.

5. The resist composition of claim 1, further comprising (E) a basic
compound.

6. The resist composition of claim 1, further comprising (F) a dissolution
inhibitor.

7. A pattern forming process comprising the steps of (1) applying the
resist composition of claim 1 onto a substrate to form a resist coating,
(2) heat treating the resist coating and exposing it to high-energy
radiation through a photomask, and (3) developing the exposed coating
with a developer.

8. A pattern forming process comprising the steps of (1) applying the
resist composition of claim 1 onto a substrate to form a resist coating,
(2) heat treating the resist coating and exposing it to high-energy
radiation from a projection lens through a photomask while holding a
liquid between the substrate and the projection lens, and (3) developing
the exposed coating with a developer.

9. A pattern forming process comprising the steps of (1) applying the
resist composition of claim 1 onto a substrate to form a resist coating,
(2) forming a protective coating onto the resist coating, (3) heat
treating and exposing the coated substrate to high-energy radiation from
a projection lens through a photomask while holding a liquid between the
substrate and the projection lens, and (4) developing with a developer.

10. The process of claim 8 wherein the liquid is water.

11. The process of claim 7 wherein the high-energy radiation has a
wavelength in the range of 180 to 250 nm.

12. A pattern forming process comprising the steps of (1) applying the
resist composition of claim 1 onto a mask blank to form a resist coating,
(2) heat treating and exposing the resist coating in vacuum to electron
beam, and (3) developing with a developer.

Description:

CROSS-REFERENCE TO RELATED APPLICATION

[0001]This non-provisional application claims priority under 35 U.S.C.
§119(a) on Patent Application No. 2008-124476 filed in Japan on May
12, 2008, the entire contents of which are hereby incorporated by
reference.

TECHNICAL FIELD

[0002]This invention generally relates to a photolithography process for
the microfabrication of semiconductor devices, and particularly to an
immersion photolithography process involving directing ArF excimer laser
radiation having a wavelength of 193 nm from a projection lens toward a
resist-coated substrate, with a liquid (e.g., water) intervening between
the lens and the substrate. More particularly, it relates to a resist
composition for use in the lithography process and a process for forming
a pattern using the same.

BACKGROUND ART

[0003]In the recent drive for higher integration and operating speeds in
LSI devices, the pattern rule is made drastically finer. The background
supporting such a rapid advance is a reduced wavelength of the light
source for exposure. The change-over from i-line (365 nm) of a mercury
lamp to shorter wavelength KrF laser (248 nm) enabled mass-scale
production of dynamic random access memories (DRAM) with an integration
degree of 64 MB (processing feature size≦0.25 μm). To establish
the micropatterning technology necessary for the fabrication of DRAM with
an integration degree of 256 MB and 1 GB or more, the lithography using
ArF excimer laser (193 nm) is under active investigation. The ArF excimer
laser lithography, combined with a high NA lens (NA≧0.9), is
considered to comply with 65-nm node devices. For the fabrication of next
45-nm node devices, the F2 laser lithography of 157 nm wavelength
became a candidate. However, because of many problems including a cost
and a shortage of resist performance, the employment of F2
lithography was postponed. ArF immersion lithography was proposed as a
substitute for the F2 lithography. Efforts have been made for the
early introduction of ArF immersion lithography (see Proc. SPIE, Vol.
4690, xxix, 2002).

[0004]In the ArF immersion lithography, the space between the projection
lens and the wafer is filled with water and ArF excimer laser is
irradiated through the water. Since water has a refractive index of 1.44
at 193 nm, pattern formation is possible even using a lens with NA of 1.0
or greater. Theoretically, it is possible to increase the NA to 1.44. The
resolution is improved by an increment of NA. A combination of a lens
having NA of at least 1.2 with ultra-high resolution technology suggests
a way to the 45-nm node (see Proc. SPIE, Vol. 5040, p 724, 2003).

[0005]Several problems arise when a resist film is exposed in the presence
of water. For example, the acid once generated from a photoacid generator
and a basic compound added to the resist material can be partially
leached in water. As a result, pattern profile changes and pattern
collapse can occur. It is also pointed out that water droplets remaining
on the resist film, though in a minute volume, can penetrate into the
resist film to generate defects.

[0006]These drawbacks of the ArF immersion lithography may be overcome by
providing a protective coating between the resist film and water to
prevent resist components from being leached out and water from
penetrating into the resist film (see 2nd Immersion Workshop: Resist and
Cover Material Investigation for Immersion Lithography, 2003).

[0007]With respect to the protective coating on the photoresist film, a
typical antireflective coating on resist (ARCOR) process is disclosed in
JP-A 62-62520, JP-A 62-62521, and JP-A 60-38821. The ARCs are made of
fluorinated compounds having a low refractive index, such as
perfluoroalkyl polyethers and perfluoroalkyl amines. Since these
fluorinated compounds are less compatible with organic substances,
fluorocarbon solvents are used in coating and stripping of protective
coatings, raising environmental and cost issues.

[0008]Other resist protective coating materials under investigation
include water-soluble or alkali-soluble materials. See, for example, JP-A
6-273926, Japanese Patent No. 2,803,549, and J. Photopolymer Sci. and
Technol., Vol. 18, No. 5, p 615, 2005. Since the alkali-soluble resist
protective coating material is strippable with an alkaline developer, it
eliminates a need for an extra stripping unit and offers a great cost
saving. From this standpoint, great efforts have been devoted to develop
water-insoluble resist protective coating materials, for example, resins
having alkali-soluble groups such as fluorinated alcohol, carboxyl or
sulfo groups on side chains. See WO 2005/42453, WO 2005/69676, JP-A
2005-264131, JP-A 2006-133716, and JP-A 2006-91798.

[0009]As means for preventing resist components from being leached out and
water from penetrating into the resist film without a need for a
protective coating material, it is proposed in JP-A 2006-48029, JP-A
2006-309245, and JP-A 2007-187887 to add an alkali-soluble, hydrophobic
compound as a surfactant to the resist material. This method achieves
equivalent effects to the use of resist protective coating material
because the hydrophobic compound is segregated at the resist surface
during resist film formation. Additionally, this method is economically
advantageous over the use of a resist protective film because steps of
forming and stripping the protective film are unnecessary.

[0010]The ArF immersion lithography systems commercially available at the
present are designed such that water is partly held between the
projection lens and the wafer rather than immersing the resist-coated
substrate fully in water, and exposure is carried out by scanning the
wafer-holding stage at a speed of 300 to 550 nm/sec. In the event of such
high-speed scanning, unless the performance of the resist or protective
film is sufficient, water cannot be held between the projection lens and
the wafer, and water droplets are left on the surface of the resist film
or protective film after scanning. It is believed that residual droplets
cause defective pattern formation.

[0011]To eliminate the droplets remaining on the surface of the
photoresist or protective film after scanning, it is necessary to improve
the flow or mobility of water (hereinafter, water slip) on the relevant
coating film. It is reported that the number of defects associated with
the immersion lithography can be reduced by increasing the receding
contact angle of the photoresist or protective film with water. See 2nd
International Symposium on Immersion Lithography, Sep. 12-15, 2005,
Defectivity data taken with a full-field immersion exposure tool, Nakano
et al.

[0012]One exemplary material known to have excellent water slip and water
repellency on film surface is a copolymer of
α-trifluoromethylacrylate and norbornene derivative (Proc. SPIE,
Vol. 4690, p 18, 2002). While this polymer was developed as the base
resin for F2 (157 nm) lithography resist materials, it is
characterized by a regular arrangement of molecules of
α-trifluoromethylacrylate (effective for water repellency
improvement) and norbornene derivative in a ratio of 2:1.

[0013]When a water molecule interacts with methyl and trifluoromethyl
groups, it orients via its oxygen and hydrogen atoms, respectively, and
the orientation distance between water and methyl is longer, as discussed
in XXIV FATIPEC Congress Book, Vol. B, p 15 (1997) and Progress in
Organic Coatings, 31, p 97-104 (1997). A resin having not only water
repellent fluorinated units introduced, but also both fluoroalkyl and
alkyl groups incorporated is improved in water slip because of a longer
orientation distance of water. In fact, a polymer having a regular
arrangement of water repellent monomeric units like the above-referred
copolymer of α-trifluoromethylacrylate and norbornene derivative is
used as the base polymer in a protective coating for immersion
lithography, water slip is drastically improved (see US 20070122736 or
JP-A 2007-140446).

[0014]A material having good water slip performance is also required from
the standpoint of productivity. The immersion lithography needs higher
throughputs than ever. For improved productivity, the exposure time must
be reduced, which in turn requires high-speed scanning operation of the
stage. In order to move the stage at a high speed while holding water
beneath the lens, it is desired to have a resist material or resist
protective film having higher water slip performance.

[0015]The highly water repellent/water slippery materials discussed above
are expected to be applied not only to the ArF immersion lithography, but
also to the resist material for mask blanks. Resist materials for mask
blanks suffer from problems including a change of sensitivity during
long-term exposure in vacuum and long-term stability after coating. With
respect to the control of sensitivity changes in vacuum, an improvement
is made by a combination of acid labile groups of acetal and tertiary
ester types (U.S. Pat. No. 6,869,744). It is believed that after coating
of a resist material, an amine component is adsorbed to the resist film
surface whereby the resist varies its sensitivity or profile. A method of
modifying the surface of a resist film for preventing adsorption of an
amine component to the resist film has been devised.

[0016]Hydrophobic surfactants for use in resist protective coatings and
resist materials are allegedly effective in overcoming a pattern profile
change, referred to as "dark-bright difference," which is considered
problematic in many types of lithography including immersion lithography,
dry lithography and EB lithography. The dark-bright difference is a
phenomenon that the profile of a line-and-space pattern differs between a
bright pattern where a peripheral portion around the pattern is exposed
and a dark pattern where a peripheral portion around the pattern is not
exposed. When a peripheral portion around the pattern is exposed, the
acid generated in the peripheral portion can evaporate during PEB to
cover the pattern area, whereby the line pattern undergoes a film
slimming. When a peripheral portion around the pattern is not exposed, no
acid is supplied from the peripheral portion and inversely, amine
evaporates whereby the line pattern takes a bulged top profile. The
"dark-bright difference" occurs by this mechanism. The dark-bright
difference can be reduced by providing a protective coating on the resist
film.

[0017]An object of the invention is to provide a resist composition which
has improved water repellency and water slip and suffer from few
development defects; an additive polymer essential to achieve such
performance; and a pattern forming process using the composition.

[0018]The inventors have discovered that a copolymer of an alkali-soluble
(α-trifluoromethyl)acrylate and a norbornene derivative, designated
polymer P1, P1', P1'' or P2 (collectively referred to as polymer PA) is
useful as an additive to a photoresist composition for immersion
lithography.

[0019]Accordingly, the present invention provides a resist composition and
a pattern forming process, as defined below.

[0020]In a first aspect, the invention provides a resist composition
comprising (A) a polymer P1 comprising repeat units of the following
general formulae (1a) and (2a), (B) a polymer having a structure
containing one or both of a lactone ring and a hydroxyl group, and/or a
structure derived from maleic anhydride, which polymer becomes soluble in
an alkaline developer under the action of an acid, (C) a compound capable
of generating an acid upon exposure to high-energy radiation, and (D) an
organic solvent.

##STR00001##

Herein R1a and R1b are hydrogen or straight, branched or cyclic
C1-C10 alkyl, R1a and R1b may bond together to form a
non-aromatic ring with the carbon atom to which they are attached,
R2 is hydrogen, methyl or trifluoromethyl, R3 is hydrogen or an
acid labile group, a1 and b1 are numbers satisfying 0<a1<1,
0<b1<1, and 0<a1+b1≦1.

[0021]In a second aspect, the invention provides a resist composition
comprising (A) a polymer P1' comprising repeat units of the following
general formulae (1a), (1b) and (2a), (B) a polymer having a structure
containing one or both of a lactone ring and a hydroxyl group, and/or a
structure derived from maleic anhydride, which polymer becomes soluble in
an alkaline developer under the action of an acid, (C) a compound capable
of generating an acid upon exposure to high-energy radiation, and (D) an
organic solvent.

##STR00002##

Herein R1a, R1b, R2 and R3 are as defined above,
R4a to R4c are hydrogen or straight, branched or cyclic
C1-C10 alkyl, and a1, a2 and b1 are numbers satisfying
0<a1<1, 0<a2<1, 0<b1<1, and 0<a1+a2+b1≦1.

[0022]In a third aspect, the invention provides a resist composition
comprising (A) a polymer P1'' comprising repeat units of the following
general formulae (1a), (1b), (2a) and (2b), (B) a polymer having a
structure containing one or both of a lactone ring and a hydroxyl group,
and/or a structure derived from maleic anhydride, which polymer becomes
soluble in an alkaline developer under the action of an acid, (C) a
compound capable of generating an acid upon exposure to high-energy
radiation, and (D) an organic solvent.

[0023]In a fourth aspect, the invention provides a resist composition
comprising (A) a polymer P2 corresponding to a polymer P1-H comprising
repeat units of the following general formulae (1a) and (2a') wherein
some or all of hydroxyl groups in formulae (1a) and (2a') are protected
with protective groups, (B) a polymer having a structure containing one
or both of a lactone ring and a hydroxyl group, and/or a structure
derived from maleic anhydride, which polymer becomes soluble in an
alkaline developer under the action of an acid, (C) a compound capable of
generating an acid upon exposure to high-energy radiation, and (D) an
organic solvent.

##STR00004##

Herein R1a, R1b, R2, a1 and b1 are as defined above.

[0024]In any of the foregoing aspects, the resist composition may further
comprise (E) a basic compound and/or (F) a dissolution inhibitor.

[0025]In a fifth aspect, the invention provides

[0026]a pattern forming process comprising the steps of (1) applying the
resist composition defined above onto a substrate to form a resist
coating, (2) heat treating the resist coating and exposing it to
high-energy radiation through a photomask, and (3) developing the exposed
coating with a developer;

[0027]a pattern forming process comprising the steps of (1) applying the
resist composition defined above onto a substrate to form a resist
coating, (2) heat treating the resist coating and exposing it to
high-energy radiation from a projection lens through a photomask while
holding a liquid between the substrate and the projection lens, and (3)
developing the exposed coating with a developer; and

[0028]a pattern forming process comprising the steps of (1) applying the
resist composition defined above onto a substrate to form a resist
coating, (2) forming a protective coating onto the resist coating, (3)
heat treating and exposing the coated substrate to high-energy radiation
from a projection lens through a photomask while holding a liquid between
the substrate and the projection lens, and (4) developing with a
developer.

[0029]Typically, the liquid is water; and the high-energy radiation has a
wavelength in the range of 180 to 250 nm.

[0030]Also provided is a pattern forming process comprising the steps of
(1) applying the resist composition defined above onto a mask blank to
form a resist coating, (2) heat treating and exposing the resist coating
in vacuum to electron beam, and (3) developing with a developer.

ADVANTAGEOUS EFFECTS OF INVENTION

[0031]When applied to the immersion lithography, the resist composition of
the invention forms a resist film having a large receding contact angle
enough to inhibit leaching-out of resist components and penetration of
water into the resist film. It also ensures that the resist film is
developed into a satisfactorily profiled pattern with minimal development
defects.

[0033]The notation (Cn-Cm) means a group containing from n to m carbon
atoms per group.

A. Polymer

[0034]The polymers P1, P1' and P1'' used in the resist composition of the
invention are characterized by comprising repeat units having the general
formulae (1a), (1b), (2a), and (2b).

##STR00005##

Herein R1a and R1b are hydrogen or straight, branched or cyclic
C1-C10 alkyl, or R1a and R1b may bond together to
form a non-aromatic ring with the carbon atom to which they are attached.
R2 is hydrogen, methyl or trifluoromethyl. R3 is hydrogen or an
acid labile group. R4a to R4c are hydrogen or straight,
branched or cyclic C1-C10 alkyl. R5 is straight, branched
or cyclic C1-C10 alkyl. The subscripts a1, a2, b1 and b2 are
numbers satisfying 0<a1<1, 0<a2<1, 0<b1<1,
0<b2<1, 0<a1+a2<1, 0<b1+b2<1, and
0<a1+a2+b1+b2≦1.

[0035]The meaning of a1+a2+b1+b2=1 is that in a polymer comprising repeat
units (1a), (1b), (2a) and (2b), the total of repeat units (1a), (1b),
(2a) and (2b) is 100 mol % based on the total amount of entire repeat
units. The sum of fractions of repeat units (1a) and (1b) is preferably
20 to 80 mol %, and more preferably 30 to 70 mol %. The meaning of
a1+a2+b1+b2<1 is that the total of repeat units (1a), (1b), (2a) and
(2b) is less than 100 mol % based on the total amount of entire repeat
units, indicating the inclusion of other repeat units.

[0036]In formulae (1b), (2a) and (2b), exemplary straight, branched or
cyclic C1-C10 alkyl groups represented by R1a, R1b,
R4a to R4c, and R5 include, but are not limited to,
methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl,
tert-amyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl,
cyclopentyl, cyclohexyl, cyclopentylmethyl, cyclopentylethyl,
cyclopentylbutyl, cyclohexylmethyl, cyclohexylethyl, cyclohexylbutyl, and
adamantyl. R1a and R1b may bond together to form a non-aromatic
ring with the carbon atom to which they are attached, wherein each of
R1a and R1b is alkylene, examples of which include the
foregoing alkyl groups with one hydrogen atom eliminated, and exemplary
rings include cyclopentyl and cyclohexyl.

[0037]The acid labile group represented by R3 in formula (2a) may be
selected from a variety of such groups. Examples of the acid labile group
are groups of the following general formulae (L1) to (L4), tertiary alkyl
groups of 4 to 20 carbon atoms, preferably 4 to 15 carbon atoms,
trialkylsilyl groups in which each alkyl moiety has 1 to 6 carbon atoms,
and oxoalkyl groups of 4 to 20 carbon atoms.

##STR00006##

[0038]Herein, the broken line denotes a valence bond. In formula (L1),
RL01 and RL02 are hydrogen or straight, branched or cyclic
alkyl groups of 1 to 18 carbon atoms, preferably 1 to 10 carbon atoms.
Exemplary alkyl groups include methyl, ethyl, propyl, isopropyl, n-butyl,
sec-butyl, tert-butyl, cyclopentyl, cyclohexyl, 2-ethylhexyl, n-octyl,
and adamantyl. RL03 is a monovalent hydrocarbon group of 1 to 18
carbon atoms, preferably 1 to 10 carbon atoms, which may contain a
heteroatom such as oxygen, examples of which include unsubstituted
straight, branched or cyclic alkyl groups and substituted forms of such
alkyl groups in which some hydrogen atoms are replaced by hydroxyl,
alkoxy, oxo, amino, alkylamino or the like. Illustrative examples of the
straight, branched or cyclic alkyl groups are as exemplified above for
RL01 and RL02, and examples of the substituted alkyl groups are
as shown below.

##STR00007##

[0039]A pair of RL01 and RL02, RL01 and RL03, or
RL02 and RL03 may bond together to form a ring with carbon and
oxygen atoms to which they are attached. Each of ring-forming RL01,
RL02 and RL03 is a straight or branched alkylene group of 1 to
18 carbon atoms, preferably 1 to 10 carbon atoms when they form a ring.

[0040]In formula (L2), RL04 is a tertiary alkyl group of 4 to 20
carbon atoms, preferably 4 to 15 carbon atoms, a trialkylsilyl group in
which each alkyl moiety has 1 to 6 carbon atoms, an oxoalkyl group of 4
to 20 carbon atoms, or a group of formula (L1). Exemplary tertiary alkyl
groups are tert-butyl, tert-amyl, 1,1-diethylpropyl,
2-cyclopentylpropan-2-yl, 2-cyclohexylpropan-2-yl,
2-(bicyclo[2.2.1]heptan-2-yl)propan-2-yl, 2-(adamantan-1-yl)propan-2-yl,
1-ethylcyclopentyl, 1-butylcyclopentyl, 1-ethylcyclohexyl,
1-butylcyclohexyl, 1-ethyl-2-cyclopentenyl, 1-ethyl-2-cyclohexenyl,
2-methyl-2-adamantyl, 2-ethyl-2-adamantyl, and the like. Exemplary
trialkylsilyl groups are trimethylsilyl, triethylsilyl, and
dimethyl-tert-butylsilyl. Exemplary oxoalkyl groups are 3-oxocyclohexyl,
4-methyl-2-oxooxan-4-yl, and 5-methyl-2-oxooxolan-5-yl. Letter y is an
integer of 0 to 6.

[0041]In formula (L3), RL05 is an optionally substituted, straight,
branched or cyclic C1-C10 alkyl group or an optionally
substituted C6-C20 aryl group. Examples of the optionally
substituted alkyl groups include straight, branched or cyclic alkyl
groups such as methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl,
tert-butyl, tert-amyl, n-pentyl, n-hexyl, cyclopentyl, cyclohexyl, and
bicyclo[2.2.1]heptyl, and substituted forms of such groups in which some
hydrogen atoms are replaced by hydroxyl, alkoxy, carboxy, alkoxycarbonyl,
oxo, amino, alkylamino, cyano, mercapto, alkylthio, sulfo or other groups
or in which some methylene groups are replaced by oxygen or sulfur atoms.
Examples of optionally substituted aryl groups include phenyl,
methylphenyl, naphthyl, anthryl, phenanthryl, and pyrenyl. Letter m is
equal to 0 or 1, n is equal to 0, 1, 2 or 3, and 2m+n is equal to 2 or 3.

[0042]In formula (L4), RL06 is an optionally substituted, straight,
branched or cyclic C1-C10 alkyl group or an optionally
substituted C6-C20 aryl group. Examples of these groups are the
same as exemplified for RL05. RL07 to RL16 independently
represent hydrogen or monovalent hydrocarbon groups of 1 to 15 carbon
atoms. Exemplary hydrocarbon groups are straight, branched or cyclic
alkyl groups such as methyl, ethyl, propyl, isopropyl, n-butyl,
sec-butyl, tert-butyl, tert-amyl, n-pentyl, n-hexyl, n-octyl, n-nonyl,
n-decyl, cyclopentyl, cyclohexyl, cyclopentylmethyl, cyclopentylethyl,
cyclopentylbutyl, cyclohexylmethyl, cyclohexylethyl and cyclohexylbutyl,
and substituted forms of these groups in which some hydrogen atoms are
replaced by hydroxyl, alkoxy, carboxy, alkoxycarbonyl, oxo, amino,
alkylamino, cyano, mercapto, alkylthio, sulfo or other groups.
Alternatively, two of RL07 to RL16 may bond together to form a
ring with the carbon atom(s) to which they are attached (for example, a
pair of RL07 and RL08, RL07 and RL09, RL08 and
RL10, RL09 and RL10, RL11 and RL12, RL13
and RL14, or a similar pair form a ring). Each of RL07 to
RL16 represents a divalent C1-C15 hydrocarbon group when
they form a ring, examples of which are those exemplified above for the
monovalent hydrocarbon groups, with one hydrogen atom being eliminated.
Two of RL07 to RL16 which are attached to vicinal carbon atoms
may bond together directly to form a double bond (for example, a pair of
RL07 and RL09, RL09 and RL15, RL13 and
RL15, or a similar pair).

[0043]Of the acid labile groups of formula (L1), the straight and branched
ones are exemplified by the following groups.

[0047]Of the acid labile groups of formula (L4), those groups of the
following formulae (L4-1) to (L4-4) are preferred.

##STR00010##

[0048]In formulas (L4-1) to (L4-4), the broken line denotes a bonding site
and direction. RL41 is each independently a monovalent hydrocarbon
group, typically a straight, branched or cyclic C1-C10 alkyl
group, such as methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl,
tert-butyl, tert-amyl, n-pentyl, n-hexyl, cyclopentyl and cyclohexyl.

[0049]For formulas (L4-1) to (L4-4), there can exist enantiomers and
diastereomers. Each of formulae (L4-1) to (L4-4) collectively represents
all such stereoisomers. Such stereoisomers may be used alone or in
admixture.

[0050]For example, the general formula (L4-3) represents one or a mixture
of two selected from groups having the following general formulas
(L4-3-1) and (L4-3-2).

##STR00011##

Note that RL41 is as defined above.

[0051]Similarly, the general formula (L4-4) represents one or a mixture of
two or more selected from groups having the following general formulas
(L4-4-1) to (L4-4-4).

##STR00012##

Note that RL41 is as defined above.

[0052]Each of formulas (L4-1) to (L4-4), (L4-3-1) and (L4-3-2), and
(L4-4-1) to (L4-4-4) collectively represents an enantiomer thereof and a
mixture of enantiomers.

[0053]It is noted that in the above formulas (L4-1) to (L4-4), (L4-3-1)
and (L4-3-2), and (L4-4-1) to (L4-4-4), the bond direction is on the exo
side relative to the bicyclo[2.2.1]heptane ring, which ensures high
reactivity for acid catalyzed elimination reaction (see JP-A
2000-336121). In preparing these monomers having a tertiary exo-alkyl
group of bicyclo[2.2.1]heptane structure as a substituent group, there
may be contained monomers substituted with an endo-alkyl group as
represented by the following formulas (L4-1-endo) to (L4-4-endo). For
good reactivity, an exo proportion of at least 50 mol % is preferred,
with an exo proportion of at least 80 mol % being more preferred.

##STR00013##

Note that RL41 is as defined above.

[0054]Illustrative examples of the acid labile group of formula (L4) are
given below

##STR00014##

[0055]Examples of the tertiary C4-C20 alkyl groups,
trialkylsilyl groups in which each alkyl moiety has 1 to 6 carbon atoms,
and C4-C20 oxoalkyl groups, represented by R3, are as
exemplified for RL04 and the like.

[0056]In the resist composition of the fourth aspect, the base polymer may
be a polymer P2 corresponding to a polymer P1-H comprising repeat units
of the general formulae (1a) and (2a') as essential units wherein some or
all of hydroxyl groups in either one or both of formula (1a) and formula
(2a') are protected with protective groups. It is acceptable that some or
all hydroxyl groups in formulae (1a) and (2a') be protected with
protective groups.

##STR00015##

Herein R1a and R1b are hydrogen or straight, branched or cyclic
C1-C10 alkyl, or R1a and R1b may bond together to
form a non-aromatic ring with the carbon atom to which they are attached.
R2 is hydrogen, methyl or trifluoromethyl. The subscripts a1 and b1
are numbers satisfying 0<a1<1, 0<b1<1, and
0<a1+b1≦1.

[0057]As in the foregoing embodiment, the meaning of a1+b1=1 is that the
total of repeat units (1a) and (2a') is 100 mol % based on the total
amount of entire repeat units. A proportion of repeat units (1a) is
preferably 20 to 80 mol %, and more preferably 30 to 70 mol %. The
meaning of a1+b1<1 is that the total of repeat units (1a) and (2a') is
less than 100 mol % based on the total amount of entire repeat units,
indicating the inclusion of other repeat units.

[0058]In formula (2a'), exemplary straight, branched or cyclic
C1-C10 alkyl groups represented by R1a and R1b
include, but are not limited to, methyl, ethyl, n-propyl, isopropyl,
n-butyl, sec-butyl, tert-butyl, tert-amyl, n-pentyl, n-hexyl, n-heptyl,
n-octyl, n-nonyl, n-decyl, cyclopentyl, cyclohexyl, cyclopentylmethyl,
cyclopentylethyl, cyclopentylbutyl, cyclohexylmethyl, cyclohexylethyl,
cyclohexylbutyl, and adamantyl. R1a and R1b may bond together
to form a ring as described above, wherein each of R1a and R1b
is alkylene, examples of which include the foregoing alkyl groups with
one hydrogen atom eliminated, and suitable rings are as exemplified
above.

[0060]In the polymer P2, a degree of protection of hydroxyl groups on
polymer P1-H may vary from 0 mol % to 100 mol % of the entire hydroxyl
groups. As a degree of protection is increased, water slip performance
such as sliding angle and receding contact angle can be enhanced.
However, an excessive increase in degree of protection results in a resin
having a reduced alkali dissolution rate. In practice, a polymer having a
degree of protection of hydroxyl groups in the range of 0 to 60 mol %,
and preferably 10 to 40 mol % is used for a balance of water slip
performance and alkali dissolution rate.

[0061]Illustrative, non-limiting examples of the repeat units of formula
(1b) are given below.

##STR00016##

[0062]Illustrative, non-limiting examples of the repeat units of formula
(2a) are given below.

##STR00017## ##STR00018##

Herein R2 and R3 are as defined above.

[0063]Illustrative, non-limiting examples of the repeat units of formula
(2b) are given below.

##STR00019## ##STR00020##

Herein R2 is as defined above.

[0064]In polymer PA used in the resist composition of the invention, the
repeat unit of formula (1a) contributes to water repellency and alkali
solubility since it contains a hexafluoroalcohol group. The repeat units
of formulae (1b), (2a) and (2b) exert excellent performance in water
repellency and water slip despite poor alkali solubility. Because of a
combination of these units, polymer PA exhibits excellent performance in
water repellency and water slip.

[0065]It is believed that the regular arrangement of
α-trifluoromethylacrylate structures and norbornene structures also
contributes to the excellent water slip of polymer PA.

[0066]As discussed in the literature listed above, a water molecule
orients via its oxygen atom upon interaction with a methyl group, whereas
it orients via its hydrogen atom upon interaction with a trifluoromethyl
group. It is reported in XXIV FATIPEC Congress Book, Vol. B, p 15 (1997)
that the distances between H (methyl) and O (water molecule) and between
F (trifluoromethyl) and H (water molecule) in these orientations are
0.252 nm and 0.187 nm, respectively. For better water slip performance, a
longer orientation distance of a water molecule is advantageous. The
above fact implies that mere introduction of fluorine into a resin fails
to increase the orientation distance of a water molecule and does not
lead to a dramatic improvement in water slip performance.

[0067]In contrast, in a system where methyl and trifluoromethyl groups are
regularly arranged, for example, if one hydrogen atom of a water molecule
orients to a trifluoromethyl group, the other hydrogen atom of water
molecule is present in proximity to an adjacent methyl group, so that a
repulsion force develops between H (methyl) and H (water molecule). As a
result, the distance of orientation to water increases to provide an
improvement in water slip performance. For the same reason, polymers
having a regular arrangement of α-trifluoromethylacrylate
structures and norbornene structures like polymer PA exhibit better water
slip performance than polymers wherein trifluoromethyl groups are
randomly distributed within the polymer structure (e.g., methacrylate
polymers).

[0068]The scanning operation in the immersion lithography requires a high
receding contact angle in order to prevent liquid droplets from being
left backward of scanning and a low advancing contact angle in order to
restrain micro-bubbles from being entrained forward of scanning. This
necessitates a material having a little difference between advancing and
receding contact angles. Polymer PA is believed promising as a
hydrophobic additive for a resist material in the immersion lithography
since it offers so small a sliding angle of a water droplet that it
causes little deformation of a water droplet and has a little difference
between advancing and receding contact angles.

[0069]Although polymer PA used in the resist composition of the invention
may exert satisfactory performance by a combination of repeat units of
formulae (1a), (1b), (2a), and (2b), they may also be constructed by
further combining with repeat units of one or more type of the general
formulae (7a) to (7e), (8a) to (8e), (9a) to (9c), and (10a) to (10c),
shown below, for the purposes of imparting additional water repellency
and water slip and controlling alkali solubility and developer affinity.

##STR00021## ##STR00022## ##STR00023##

Herein R13 is C1-C10 alkyl or fluoroalkyl; R14 is an
adhesive group; R15 is an acid labile group; R16 is a single
bond or a divalent C1-C10 organic group; R17 and R18
are each hydrogen, methyl or trifluoromethyl.

[0071]In formulae (7b) and (8b), the adhesive group represented by
R14 may be selected from a variety of such groups, typically those
groups shown below.

##STR00024## ##STR00025## ##STR00026##

Herein, the broken line designates a valence bond.

[0072]In formulae (7c) and (8c), the acid labile group represented by
R15 may be selected from those groups illustrated for R3.

[0073]In formulae (7e), (8e), and (9a) to (9c), suitable divalent organic
groups represented by R16 include alkylene groups such as methylene
and groups of the following formulae.

##STR00027##

Herein, the broken line designates a valence bond.

[0074]The polymer PA used in the resist composition may be synthesized by
general polymerization processes including radical polymerizataion using
initiators such as 2,2'-azobisisobutyronitrile (AIBN), and ionic (or
anionic) polymerization using alkyllithium or the like. The
polymerization may be carried out by its standard technique. Preferably
the polymers are prepared by radical polymerization while the
polymerization conditions may be determined in accordance with the type
of initiator, temperature, pressure, concentration, solvent, additives,
and the like.

[0075]Examples of the radical polymerization initiator used herein include
azo compounds such as 2,2'-azobisisobutyronitrile (AIBN),
2,2'-azobis(4-methoxy-2,4-dimethylvaleronitrile),
2,2'-azobis(2,4-dimethylvaleronitrile),
2,2'-azobis(2,4,4-trimethylpentane), and dimethyl
2,2'-azobis(isobutyrate); peroxides such as tert-butylperoxypivalate,
lauroyl peroxide, benzoyl peroxide, and tert-butylperoxylaurate;
water-soluble polymerization initiators such as potassium persulfate; and
redox initiators comprising a peroxide (e.g., potassium persulfate or
hydrogen peroxide) combined with a reducing agent (e.g., sodium sulfite).
Although the amount of polymerization initiator used may vary with its
type and other polymerization conditions, it is generally used in an
amount of 0.001 to 10 mol %, and preferably 0.01 to 5 mol % based on the
total moles of monomers to be polymerized.

[0076]During the synthesis of polymer PA, any known chain transfer agent
such as dodecyl mercaptan or 2-mercaptoethanol may be added for molecular
weight control purpose. The amount of chain transfer agent added is
preferably 0.01 to 10 mol % based on the total moles of monomers to be
polymerized.

[0077]While polymer PA may be synthesized by combining suitable monomers
selected from polymerizable monomers corresponding to repeat units of
formulae (1a), (1b), (2a), (2b), (7a) to (7e), (8a) to (8e), (9a) to
(9c), and (10a) to (10c), adding an initiator and chain transfer agent to
the monomer mixture, and effecting polymerization, a solvent may be used
if necessary. Any solvent may be used as long as it does not interfere
with the desired polymerization reaction. Typical solvents used herein
include esters such as ethyl acetate, n-butyl acetate, and
γ-butyrolactone; ketones such as acetone, methyl ethyl ketone, and
methyl isobutyl ketone; aliphatic or aromatic hydrocarbons such as
toluene, xylene and cyclohexane; alcohols such as isopropyl alcohol and
ethylene glycol monomethyl ether; and ether solvents such as diethyl
ether, dioxane, and tetrahydrofuran, which may be used alone or in
admixture. Although the amount of solvent used may vary with the desired
degree of polymerization (or molecular weight), the amount of initiator
added, and other polymerization conditions such as polymerization
temperature, it is generally used in such an amount as to provide a
concentration of 0.1 to 95% by weight, preferably 5 to 90% by weight of
monomers to be polymerized.

[0078]Although the temperature of the polymerization reaction may vary
with the identity of polymerization initiator or the boiling point of
solvent, it is preferably in the range of 20 to 200° C., and more
preferably 50 to 140° C. Any desired reactor or vessel may be used
for the polymerization reaction.

[0079]From the solution or dispersion of the polymer thus synthesized, the
organic solvent or water serving as the reaction medium is removed by any
well-known techniques. Suitable techniques include, for example,
re-precipitation followed by filtration, and heat distillation under
vacuum.

[0080]Polymer P2 used herein may be synthesized by synthesizing a polymer
P1-H comprising repeat units of formulae (1a) and (2a'), then effecting
post-protection reaction to substitute for some or all hydroxyl groups.

##STR00028##

Herein, R1a, R1b, R2, a1 and b1 are as defined above.

[0081]Polymer P2 is obtainable by reacting polymer P1-H with a base in an
amount of 1 to 2 equivalents relative to the desired degree of
substitution of hydroxyl groups, and then with R--X (wherein R is an acid
labile group or alkyl as mentioned above and X is chlorine, bromine or
iodine) in an amount of 1 to 2 equivalents relative to the base.

##STR00029##

[0082]The post-protection reaction may be effected in a solvent, which is
selected from hydrocarbons such as benzene and toluene, and ethers such
as dibutyl ether, diethylene glycol diethyl ether, diethylene glycol
dimethyl ether, tetrahydrofuran and 1,4-dioxane, alone or in admixture.
Suitable bases used herein include, but are not limited to, sodium
hydride, n-butyllithium, lithium diisopropylamide, triethylamine, and
pyridine.

[0083]Desirably polymers PA have a weight average molecular weight (Mw) of
1,000 to 500,000, and especially 2,000 to 30,000, as determined by gel
permeation chromatography (GPC) using polystyrene standards. This is
because a polymer with too low a Mw may be more dissolvable in water
whereas too high a Mw may interfere with film formation after spin
coating and lead to a decline of alkali solubility.

[0084]In polymer PA wherein U1 stands for a total molar number of a
monomer corresponding to units of formula (1a), U2 stands for a total
molar number of a monomer corresponding to units of formula (1b), U3
stands for a total molar number of a monomer corresponding to units of
formula (2a), and U4 stands for a total molar number of a monomer
corresponding to units of formula (2b), with the proviso that
U1+U2+U3+U4=UA, values of U1, U2, U3 and U4 are preferably determined so
as to meet:

[0085]0≦U1/UA<1, more preferably 0.2≦U1/UA≦0.7,
even more preferably 0.3≦U1/UA≦0.7,

[0086]0≦U2/UA<1, more preferably 0.1≦U2/UA≦0.7,
even more preferably 0.1≦U2/UA≦0.5,

[0087]0≦U3/UA<1, more preferably 0.1≦U3/UA≦0.6,
even more preferably 0.1≦U3/UA≦0.5, and

[0088]0≦U4/UA<1, more preferably 0≦U4/UA≦0.7, even
more preferably 0.1≦U4/UA≦0.5.

[0089]In the embodiment wherein additional repeat units of formulae (7a)
to (7e), (8a) to (8e), (9a) to (9c), (10a) to (10c) are incorporated into
the polymers for the purpose of improving their function as an additive
in the resist composition, provided that U5 stands for a total molar
number of monomers corresponding to the additional units and
U1+U2+U3+U4+U5=UA', a ratio of UA to UA' is preferably determined so as
to meet 0≦UA/UA'≦1, more preferably 0.6<UA/UA'≦1,
and even more preferably 0.8≦UA/UA'≦1.

[0090]In the first embodiment wherein polymer PA is used as an additive to
resist material, it is combined with base polymer (B) preferably in such
amounts that the amount of polymer PA is 0.1 to 50 parts, more preferably
0.5 to 10 parts by weight per 100 parts by weight of polymer (B). At
least 0.1 phr of polymer PA is effective in forming a photoresist film
having an increased receding contact angle with water on its surface. Up
to 50 phr of polymer PA ensures to form a photoresist film having a low
dissolution rate in an alkaline developer, maintaining the height of a
fine pattern formed therefrom.

B. Base Polymer

[0091]The resist composition is typically a chemically amplified positive
resist composition. Base polymer (B) to be combined with additive polymer
(A) is a polymer comprising a structure having one or both of a lactone
ring and a hydroxyl group and/or a maleic anhydride-derived structure
which becomes soluble in an alkaline developer under the action of an
acid. Suitable polymers or base resins (B) include polymers of
(meth)acrylic acid esters, copolymers of
(α-trifluoromethyl)acrylate and maleic anhydride, alternating
copolymers of cyclolefins and maleic anhydride, polynorbornene,
cycloolefin ring-opening metathesis polymerization (ROMP) polymers,
hydrogenated cycloolefin ROMP polymers, and the like.

[0092]Specifically the polymer (B) used herein includes, but is not
limited to, those polymers comprising units of the following formula (R1)
and/or (R2) and having a weight average molecular weight (Mw) of 1,000 to
100,000, and especially 3,000 to 30,000, as measured by GPC versus
polystyrene standards.

##STR00030## ##STR00031##

[0093]Herein, R001 is hydrogen, methyl, trifluoromethyl or
--CH2CO2R003; R002 is hydrogen, methyl or
--CO2R003; R003 is a straight, branched or cyclic
C1-C15 alkyl; R004 is hydrogen or a monovalent
C1-C15 hydrocarbon group having a fluorinated substituent
group, carboxyl group or hydroxyl group; at least one of R005 to
R008 represents a monovalent C1-C15 hydrocarbon group
having a fluorinated substituent group, carboxyl group or hydroxyl group
while the remaining R's independently represent hydrogen or straight,
branched or cyclic C1-C15 alkyl groups; R009 is a
monovalent C3-C15 hydrocarbon group containing a --CO2--
partial structure; at least one of R010 to R013 is a monovalent
C2-C15 hydrocarbon group containing a --CO2-- partial
structure, while the remaining R's are independently hydrogen or
straight, branched or cyclic, C1-C15 alkyl groups; R014 is
a polycyclic C7-C15 hydrocarbon group or an alkyl group
containing such a polycyclic hydrocarbon group; R015 is an acid
labile group; X is methylene or oxygen; R016 and R018 are
hydrogen or methyl; R017 is straight, branched or cyclic
C1-CB alkyl; and k is 0 or 1. In formula (R1), the subscripts
a1', a2', a3', b1', b2', b3', c1', c2', c3', d1', d2', d3', and e' are
numbers from 0 to less than 1, satisfying
a1'+a2'+a3'+b1'+b2'+b3'+c1'+c2'+c3'+d1'+d2'+d3'+e'=1. In formula (R2),
f', g', h', i', j', k', l', m' and n' are numbers from 0 to less than 1,
satisfying f'+g'+h'+i'+j'+k'+l'+m'+n'=1; x', y' and z' are each an
integer of 0 to 3, satisfying 1≦x'+y'+z'≦5 and
1≦y'+z'≦3.

[0096]R005 to R008 denote monovalent C1-C15
hydrocarbon groups having a fluorinated substituent group, carboxyl group
or hydroxyl group, examples of which include carboxy, carboxymethyl,
carboxyethyl, carboxybutyl, hydroxymethyl, hydroxyethyl, hydroxybutyl,
2-carboxyethoxycarbonyl, 4-carboxybutoxycarbonyl,
2-hydroxyethoxycarbonyl, 4-hydroxybutoxycarbonyl,
carboxycyclopentyloxycarbonyl, carboxycyclohexyloxycarbonyl,
carboxynorbornyloxycarbonyl, carboxyadamantyloxycarbonyl,
hydroxycyclopentyloxycarbonyl, hydroxycyclohexyloxycarbonyl,
hydroxynorbornyloxycarbonyl, hydroxyadamantyloxycarbonyl,
hydroxyhexafluoroisopropylcyclohexyloxycarbonyl, and
di(hydroxyhexafluoroisopropyl)cyclohexyloxycarbonyl. Examples of the
straight, branched or cyclic C1-C15 alkyl group are the same as
exemplified for R003. Alternatively, two of R005 to R008
(e.g., R005 and R006, R006 and R007) may bond
together to form a ring with the carbon atom(s) to which they are
attached. In that event, at least one of ring-forming R005 to
R008 is a divalent C1-C15 hydrocarbon group having a
fluorinated substituent group, carboxyl group or hydroxyl group, while
the remaining are independently a single bond or a straight, branched or
cyclic C1-C15 alkylene group. Examples of the divalent
C1-C15 hydrocarbon group having a fluorinated substituent
group, carboxyl group or hydroxyl group include the groups exemplified as
the monovalent hydrocarbon group having a fluorinated substituent group,
carboxyl group or hydroxyl group, with one hydrogen atom eliminated
therefrom. Examples of the straight, branched or cyclic C1-C15
alkylene groups include the groups exemplified for R003, with one
hydrogen atom eliminated therefrom.

[0097]Examples of the monovalent C3-C15 hydrocarbon group
containing a --CO2-- partial structure, represented by R009,
include 2-oxooxolan-3-yl, 4,4-dimethyl-2-oxooxolan-3-yl,
4-methyl-2-oxooxan-4-yl, 2-oxo-1,3-dioxolan-4-ylmethyl, and
5-methyl-2-oxooxolan-5-yl.

[0098]Examples of the monovalent C2-C15 hydrocarbon group
containing a --CO2-- partial structure, represented by R010 to
R013, include 2-oxooxolan-3-yloxycarbonyl,
4,4-dimethyl-2-oxooxolan-3-yloxycarbonyl,
4-methyl-2-oxooxan-4-yloxycarbonyl,
2-oxo-1,3-dioxolan-4-ylmethyloxycarbonyl, and
5-methyl-2-oxooxolan-5-yloxycarbonyl. Examples of the straight, branched
or cyclic C1-C15 alkyl groups are the same as exemplified for
R003. Alternatively, two of R010 to R013 (e.g., R010
and R011, R011 and R012) may bond together to form a ring
with the carbon atom(s) to which they are attached. In that event, at
least one of ring-forming R010 to R013 is a divalent
C2-C15 hydrocarbon group containing a --CO2-- partial
structure, while the remaining are independently a single bond or a
straight, branched or cyclic C1-C15 alkylene group. Examples of
the divalent C1-C15 hydrocarbon group containing a --CO2--
partial structure include 1-oxo-2-oxapropane-1,3-diyl,
1,3-dioxo-2-oxapropane-1,3-diyl, 1-oxo-2-oxabutane-1,4-diyl, and
1,3-dioxo-2-oxabutane-1,4-diyl, as well as the groups exemplified as the
monovalent hydrocarbon group containing a --CO2-- partial structure,
with one hydrogen atom eliminated therefrom. Examples of the straight,
branched or cyclic C1-C15 alkylene groups include the groups
exemplified for R003, with one hydrogen atom eliminated therefrom.

[0099]Examples of the polycyclic C7-C15 hydrocarbon group or the
alkyl group containing such a polycyclic hydrocarbon group, represented
by R014, include norbornyl, bicyclo[3.3.1]nonyl,
tricyclo[5.2.1.02,6]decyl, adamantyl, ethyladamantyl,
butyladamantyl, norbornylmethyl, and adamantylmethyl.

[0100]The acid labile groups represented by R015 may be selected from
a variety of such groups. Examples of the acid labile group are groups of
the general formulae (L1) to (L4), tertiary alkyl groups of 4 to 20
carbon atoms, preferably 4 to 15 carbon atoms, trialkylsilyl groups in
which each alkyl moiety has 1 to 6 carbon atoms, and oxoalkyl groups of 4
to 20 carbon atoms. Examples are the same as illustrated for the acid
labile group R3 in formula (2a).

[0101]Additionally, any of indene, norbornadiene, acenaphthylene, and
vinyl ether monomers may be copolymerized in the polymers of formulae
(R1) and (R2).

[0102]Examples of the repeat units incorporated at compositional ratio a1'
in formula (R1) are shown below, though not limited thereto.

##STR00032## ##STR00033## ##STR00034## ##STR00035##

[0103]Examples of the repeat units incorporated at compositional ratio b1'
in formula (R1) are shown below, though not limited thereto.

##STR00036## ##STR00037## ##STR00038## ##STR00039## ##STR00040##

[0104]Examples of the repeat units incorporated at compositional ratio d1'
in formula (R1) are shown below, though not limited thereto.

[0107]Furthermore, repeat units having a photosensitive sulfonium salt as
represented by the following general formula may be copolymerized with
(R1) and/or (R2) and incorporated in the polymers.

##STR00060##

Herein Rp1 is hydrogen or methyl. Rp2 is phenylene,
--O--Rp5-- or --C(═O)--X--Rp5-- wherein X is an oxygen atom
or NH, and Rp5 is a straight, branched or cyclic C1-C6
alkylene, alkenylene or phenylene group which may contain a carbonyl,
ester or ether group. Rp3 and Rp4 are each independently a
straight, branched or cyclic C1-C12 alkyl group which may
contain a carbonyl, ester or ether group, or a C6-C12 aryl
group, C1-C20 aralkyl group or thiophenyl group. X.sup.- is a
non-nucleophilic counter ion.

[0108]The polymer used as the base resin (B) is not limited to one type
and a mixture of two or more polymers may be added. The use of plural
polymers allows for easy adjustment of resist properties.

C. Acid Generator

[0109]In the resist composition of the invention, an acid generator,
specifically a compound capable of generating an acid in response to
high-energy radiation may be included in order that the resist
composition function as a chemically amplified positive resist
composition. The acid generator may be any compound capable of generating
an acid upon exposure of high-energy radiation, which is generally
referred to as "photoacid generator" or PAG. Suitable photoacid
generators include sulfonium salts, iodonium salts, sulfonyldiazomethane,
N-sulfonyloxyimide, and oxime-O-sulfonate acid generators. Exemplary acid
generators are given below while they may be used alone or in admixture
of two or more. The acid generators used herein are not limited to those
exemplified below.

[0122]Also included are the oxime sulfonates described in U.S. Pat. No.
6,916,591, for example,
(5-(4-(4-toluenesulfonyloxy)benzenesulfonyl)oxyimino-5H-thiophen-2-yliden-
e)phenylacetonitrile and
(5-(2,5-bis(4-toluenesulfonyloxy)benzenesulfonyl)oxyimino-5H-thiophen-2-y-
lidene)phenylacetonitrile.

[0124]Also included are the oxime sulfonates described in U.S. Pat. No.
6,916,591, for example,
2,2,2-trifluoro-1-(4-(3-(4-(2,2,2-trifluoro-1-(4-(4-methyl-phenylsulfonyl-
oxy)phenylsulfonyloxyimino)-ethyl)-phenoxy)-propoxy)-phenyl)ethanone
oxime(4-(4-methylphenylsulfonyloxy)-phenylsulfonate) and
2,2,2-trifluoro-1-(4-(3-(4-(2,2,2-trifluoro-1-(2,5-bis(4-methylphenylsulf-
onyloxy)benzenesulfonyloxy)phenylsulfonyloxy-imino)-ethyl)-phenoxy)-propox-
y)-phenyl)ethanone
oxime(2,5-bis(4-methylphenylsulfonyloxy)benzenesulfonyloxy)-phenylsulfona-
te).

wherein Rs1 is a substituted or unsubstituted haloalkylsulfonyl or
halobenzenesulfonyl group of 1 to 10 carbon atoms, Rs2 is a
haloalkyl group of 1 to 11 carbon atoms, and Ars1 is substituted or
unsubstituted aromatic or hetero-aromatic group, as described in WO
2004/074242.Examples include
2-[2,2,3,3,4,4,5,5-octafluoro-1-(nonafluoro-butylsulfonyloxyimino)-pentyl-
]-fluorene,
2-[2,2,3,3,4,4-pentafluoro-1-(nonafluorobutylsulfonyloxy-imino)-butyl]-fl-
uorene, 2-[2,2,3,3,4,4,5,5,6,6-decafluoro-1-(nonafluorobutylsulfonyl-oxyim-
ino)-hexyl]-fluorene,
2-[2,2,3,3,4,4,5,5-octafluoro-1-(nonafluorobutylsulfonyloxy-imino)-pentyl-
]-4-biphenyl,
2-[2,2,3,3,4,4-pentafluoro-1-(nonafluorobutylsulfonyloxy-imino)-butyl]-4--
biphenyl, and
2-[2,2,3,3,4,4,5,5,6,6-decafluoro-1-(nonafluorobutylsulfonyl-oxyimino)-he-
xyl]-4-biphenyl.

[0129]In the chemically amplified positive resist composition, an
appropriate amount of the photoacid generator is, but not limited to, 0.1
to 20 parts, and especially 0.1 to 10 parts by weight per 100 parts by
weight of the base resin (B). If the amount of the PAG is up to 20 phr,
the resulting photoresist film has a sufficiently high transmittance to
minimize a risk of degrading resolution. The PAG may be used alone or in
admixture of two or more. The transmittance of the resist film can be
controlled by using a PAG having a low transmittance at the exposure
wavelength and adjusting the amount of the PAG added.

[0130]In the resist composition, there may be added a compound which is
decomposed with an acid to generate another acid, that is, acid-amplifier
compound. For these compounds, reference should be made to J. Photopolym.
Sci. and Tech., 8, 43-44, 45-46 (1995), and ibid., 9, 29-30 (1996).

[0131]Examples of the acid-amplifier compound include
tert-butyl-2-methyl-2-tosyloxymethyl acetoacetate and
2-phenyl-2-(2-tosyloxyethyl)-1,3-dioxolane, but are not limited thereto.
Of well-known photoacid generators, many of those compounds having poor
stability, especially poor thermal stability exhibit an acid
amplifier-like behavior.

[0132]In the resist composition, an appropriate amount of the
acid-amplifier compound is up to 2 parts, and preferably up to 1 part by
weight per 100 parts by weight of the base resin (B). Up to 2 phr of the
acid-amplifier compound allows for diffusion control, minimizing a risk
of degrading resolution and pattern profile.

[0133]In addition to (A) additive polymer, (B) base resin or polymer and
(C) photoacid generator, the resist composition of the invention may
further comprise (D) an organic solvent, (E) a basic compound, and (F) a
dissolution inhibitor.

D. Solvent

[0134]The organic solvent used herein may be any organic solvent in which
the additive polymer, base resin, acid generator, and other components
are soluble. Illustrative, non-limiting, examples of the organic solvent
include ketones such as cyclohexanone and methyl-2-n-amyl ketone;
alcohols such as 3-methoxybutanol, 3-methyl-3-methoxybutanol,
1-methoxy-2-propanol, and 1-ethoxy-2-propanol; ethers such as propylene
glycol monomethyl ether, ethylene glycol monomethyl ether, propylene
glycol monoethyl ether, ethylene glycol monoethyl ether, propylene glycol
dimethyl ether, and diethylene glycol dimethyl ether; esters such as
propylene glycol monomethyl ether acetate (PGMEA), propylene glycol
monoethyl ether acetate, ethyl lactate, ethyl pyruvate, butyl acetate,
methyl 3-methoxypropionate, ethyl 3-ethoxypropionate, tert-butyl acetate,
tert-butyl propionate, and propylene glycol mono-tert-butyl ether
acetate; and lactones such as γ-butyrolactone. These solvents may
be used alone or in combinations of two or more thereof. Of the above
organic solvents, it is recommended to use diethylene glycol dimethyl
ether, 1-ethoxy-2-propanol, PGMEA, and mixtures thereof because the acid
generator is most soluble therein.

[0135]An appropriate amount of the organic solvent used is 200 to 3,000
parts, especially 400 to 2,500 parts by weight per 100 parts by weight of
the base resin (B).

E. Basic Compound

[0136]In the resist composition, an organic nitrogen-containing compound
or compounds may be compounded as the basic compound. The organic
nitrogen-containing compound used herein is preferably a compound capable
of suppressing the rate of diffusion when the acid generated by the acid
generator diffuses within the resist film. The inclusion of organic
nitrogen-containing compound holds down the rate of acid diffusion within
the resist film, resulting in better resolution. In addition, it
suppresses changes in sensitivity following exposure and reduces
substrate and environment dependence, as well as improving the exposure
latitude and the pattern profile.

[0141]In addition, organic nitrogen-containing compounds of the following
general formula (B)-1 may also be included alone or in admixture.

N(X)n(Y)3-n (B)-1

[0142]In the formula, n is equal to 1, 2 or 3; side chain Y is
independently hydrogen or a straight, branched or cyclic C1-C20
alkyl group which may contain an ether or hydroxyl group; and side chain
X is independently selected from groups of the following general formulas
(X1) to (X3), and two or three X's may bond together to form a ring.

##STR00062##

In the formulas, R300, R302 and R305 are independently
straight or branched C1-C4 alkylene groups; R301 and
R304 are independently hydrogen or a straight, branched or cyclic
C1-C20 alkyl group which may contain one or more hydroxyl,
ether, ester groups or lactone rings; R303 is a single bond or a
straight or branched C1-C4 alkylene group; and R306 is a
straight, branched or cyclic C1-C20 alkyl group which may
contain one or more hydroxyl, ether, ester groups or lactone rings.

[0148]Also included are organic nitrogen-containing compounds of imidazole
structure having a polar functional group, represented by the general
formula (B)-7.

##STR00065##

Herein, R310 is a straight, branched or cyclic alkyl group of 2 to 20
carbon atoms bearing at least one polar functional group selected from
among hydroxyl, carbonyl, ester, ether, sulfide, carbonate, cyano and
acetal groups; R311, R312 and R313 are each independently
hydrogen, a straight, branched or cyclic alkyl group, aryl group or
aralkyl group having 1 to 10 carbon atoms.

[0149]Also included are organic nitrogen-containing compounds of
benzimidazole structure having a polar functional group, represented by
the general formula (B)-8.

##STR00066##

Herein, R314 is hydrogen, a straight, branched or cyclic alkyl group,
aryl group or aralkyl group having 1 to 10 carbon atoms. R315 is a
polar functional group-bearing, straight, branched or cyclic
C1-C20 alkyl group, and the alkyl group contains as the polar
functional group at least one group selected from among ester, acetal and
cyano groups, and may additionally contain at least one group selected
from among hydroxyl, carbonyl, ether, sulfide and carbonate groups.

[0150]Further included are heterocyclic nitrogen-containing compounds
having a polar functional group, represented by the general formulae
(B)-9 and (B)-10.

##STR00067##

Herein, A is a nitrogen atom or ≡C--R322, B is a nitrogen atom
or ≡C--R323, R316 is a straight, branched or cyclic alkyl
group of 2 to 20 carbon atoms bearing at least one polar functional group
selected from among hydroxyl, carbonyl, ester, ether, sulfide, carbonate,
cyano and acetal groups; R317, R318, R319 and R320
are each independently hydrogen, a straight, branched or cyclic alkyl
group or aryl group having 1 to 10 carbon atoms, or a pair of R317
and R318 and a pair of R319 and R320, taken together, may
form a benzene, naphthalene or pyridine ring with the carbon atoms to
which they are attached; R321 is hydrogen, a straight, branched or
cyclic alkyl group or aryl group having 1 to 10 carbon atoms; R322
and R323 each are hydrogen, a straight, branched or cyclic alkyl
group or aryl group having 1 to 10 carbon atoms, or a pair of R321
and R323, taken together, may form a benzene or naphthalene ring
with the carbon atoms to which they are attached.

[0151]Also included are organic nitrogen-containing compounds of aromatic
carboxylic ester structure having the general formulae (B)-11 to (B)-14.

##STR00068##

Herein R324 is a C6-C20 aryl group or C4-C20
hetero-aromatic group, in which some or all hydrogen atoms may be
replaced by halogen atoms, straight, branched or cyclic C1-C20
alkyl groups, C6-C20 aryl groups, C7-C20 aralkyl
groups, C1-C10 alkoxy groups, C1-C10 acyloxy groups
or C1-C10 alkylthio groups. R325 is CO2R326,
OR327 or cyano group. R326 is a C1-C10 alkyl group,
in which some methylene groups may be replaced by oxygen atoms. R327
is a C1-C10 alkyl or acyl group, in which some methylene groups
may be replaced by oxygen atoms. R328 is a single bond, methylene,
ethylene, sulfur atom or --O(CH2CH2O)n-- group wherein n
is 0, 1, 2, 3 or 4. R329 is hydrogen, methyl, ethyl or phenyl. X is
a nitrogen atom or CR330. Y is a nitrogen atom or CR331. Z is a
nitrogen atom or CR332. R330, R331 and R332 are each
independently hydrogen, methyl or phenyl. Alternatively, a pair of
R330 and R331 or a pair of R331 and R332 may bond
together to form a C6-C20 aromatic ring or C2-C20
hetero-aromatic ring with the carbon atoms to which they are attached.

[0152]Further included are organic nitrogen-containing compounds of
7-oxanorbornane-2-carboxylic ester structure having the general formula
(B)-15.

##STR00069##

Herein R333 is hydrogen or a straight, branched or cyclic
C1-C10 alkyl group. R334 and R335 are each
independently a C1-C20 alkyl group, C6-C20 aryl group
or C1-C20 aralkyl group, which may contain one or more polar
functional groups selected from among ether, carbonyl, ester, alcohol,
sulfide, nitrile, amine, imine, and amide and in which some hydrogen
atoms may be replaced by halogen atoms. R334 and R335, taken
together, may form a heterocyclic or hetero-aromatic ring of 2 to 20
carbon atoms with the nitrogen atom to which they are attached.

[0153]The organic nitrogen-containing compounds may be used alone or in
admixture of two or more. The organic nitrogen-containing compound is
preferably formulated in an amount of 0.001 to 2 parts, and especially
0.01 to 1 part by weight, per 100 parts by weight of the base resin (B).
At least 0.001 phr of the nitrogen-containing compound achieves a desired
addition effect whereas up to 2 phr minimizes a risk of lowering
sensitivity.

F. Dissolution Inhibitor

[0154]The dissolution inhibitor which can be added to the resist
composition is a compound having on the molecule at least two phenolic
hydroxyl groups, in which an average of from 0 to 100 mol % of all the
hydrogen atoms on the phenolic hydroxyl groups are replaced by acid
labile groups or a compound having on the molecule at least one carboxyl
group, in which an average of 50 to 100 mol % of all the hydrogen atoms
on the carboxyl groups are replaced by acid labile groups, both the
compounds having a weight average molecular weight within a range of 100
to 1,000, and preferably 150 to 800.

[0155]The degree of substitution of the hydrogen atoms on the phenolic
hydroxyl groups with acid labile groups is on average at least 0 mol %,
and preferably at least 30 mol %, of all the phenolic hydroxyl groups.
The upper limit is 100 mol %, and preferably 80 mol %. The degree of
substitution of the hydrogen atoms on the carboxyl groups with acid
labile groups is on average at least 50 mol %, and preferably at least 70
mol %, of all the carboxyl groups, with the upper limit being 100 mol %.

[0156]Preferable examples of such compounds having two or more phenolic
hydroxyl groups or compounds having a carboxyl group include those of
formulas (D1) to (D14) below.

##STR00070## ##STR00071##

[0157]In these formulas, R201 and R202 are each hydrogen or a
straight or branched C1-C8 alkyl or alkenyl group; R203 is
hydrogen, a straight or branched C1-C8 alkyl or alkenyl group,
or --(R207)h--COOH; R204 is --(CH2)i--,
C6-C10 arylene, carbonyl, sulfonyl, an oxygen atom, or a sulfur
atom; R205 is a C1-C10 alkylene, a C6-C10
arylene, carbonyl, sulfonyl, an oxygen atom, or a sulfur atom; R206
is hydrogen, a straight or branched C1-C8 alkyl or alkenyl, or
a phenyl or naphthyl group in which at least one hydrogen atom is
substituted by a hydroxyl group; R207 is a straight or branched
C1-C10 alkylene; R208 is hydrogen or hydroxyl; h is 0 or
1, i is an integer of 2 to 10, j is an integer of 0 to 5, u is 0 or 1; s,
t, s', t', s'', and t'' are each numbers which satisfy s+t=8, s'+t'=5,
and s''+t''=4, and are such that each phenyl structure has at least one
hydroxyl group; and α is a number such that the compounds of
formula (D8) or (D9) have a weight average molecular weight of from 100
to 1,000.

[0158]Exemplary acid labile groups on the dissolution inhibitor include a
variety of such groups, typically groups of the general formulae (L1) to
(L4), tertiary C4-C20 alkyl groups, trialkylsilyl groups in
which each of the alkyls has 1 to 6 carbon atoms, and C4-C20
oxoalkyl groups. Examples of the respective groups are as previously
described.

[0159]The dissolution inhibitor may be formulated in an amount of 0 to 50
parts, preferably 0 to 40 parts, and more preferably 0 to 30 parts by
weight, per 100 parts by weight of the base resin (B), and may be used
singly or as a mixture of two or more thereof. Up to 50 parts of the
dissolution inhibitor may minimize a risk of slimming the patterned film
to invite a decline in resolution.

[0160]The dissolution inhibitor can be synthesized by introducing acid
labile groups into a compound having phenolic hydroxyl or carboxyl groups
in accordance with an organic chemical formulation.

[0161]If desired, the resist composition of the invention may further
comprise a carboxylic acid compound, acetylene alcohol derivative or
other optional ingredients. Optional ingredients may be added in
conventional amounts so long as this does not compromise the objects of
the invention.

[0162]The carboxylic acid compound used herein may be one or more
compounds selected from Groups I and II below, but is not limited
thereto. Including this compound improves the post-exposure delay (PED)
stability of the resist and ameliorates edge roughness on nitride film
substrates.

Group I:

[0163]Compounds of general formulas (A1) to (A10) below in which some or
all of the hydrogen atoms on the phenolic hydroxyl groups are replaced by
--R401--COOH (wherein R401 is a straight or branched
C1-C10 alkylene group), and in which the molar ratio C/(C+D) of
phenolic hydroxyl groups (C) to ≡C--COOH groups (D) in the molecule
is from 0.1 to 1.0.

Group II:

[0164]Compounds of general formulas (A11) to (A15) below.

##STR00072## ##STR00073##

[0165]In these formulas, R402 and R403 are each hydrogen or a
straight or branched C1-C8 alkyl or alkenyl. R404 is
hydrogen, a straight or branched C1-C8 alkyl or alkenyl, or a
--(R409)h--COOR' group wherein R' is hydrogen or
--R409--COOH. R405 is --(CH2)i-- (wherein i is 2 to
10), a C6-C10 arylene, carbonyl, sulfonyl, an oxygen atom, or a
sulfur atom. R406 is a C1-C10 alkylene, a C6-C10
arylene, carbonyl, sulfonyl, an oxygen atom, or a sulfur atom. R407
is hydrogen, a straight or branched C1-C8 alkyl or alkenyl, or
a hydroxyl-substituted phenyl or naphthyl. R408 is hydrogen or
methyl. R409 is a straight or branched C1-C10 alkylene.
R410 is hydrogen, a straight or branched C1-C8 alkyl or
alkenyl, or a --R411--COOH group wherein R411 is a straight or
branched C1-C10 alkylene. R412 is hydrogen or hydroxyl.
The letter j is a number from 0 to 3; s1, t1, s2, t2, s3, t3, s4, and t4
are each numbers which satisfy s1+t1=8, s2+t2=5, s3+t3=4, and s4+t4=6,
and are such that each phenyl structure has at least one hydroxyl group;
s5 and t5 are numbers which satisfy s5≧0, t5≧0, and
s5+t5=5; u is a number from 1 to 4; h is a number from 1 to 4; κ is
a number such that the compound of formula (A6) may have a weight average
molecular weight of 1,000 to 5,000; and λ is a number such that the
compound of formula (A7) may have a weight average molecular weight of
1,000 to 10,000.

[0166]Illustrative, non-limiting examples of the compound having a
carboxyl group include compounds of the general formulas AI-1 to AI-14
and AII-1 to AII-10 below.

##STR00074## ##STR00075## ##STR00076##

[0167]In the above formulas, R'' is hydrogen or a --CH2COOH group
such that the --CH2COOH group accounts for 10 to 100 mol % of R'' in
each compound, κ and λ are as defined above.

[0168]The compound having a ≡C--COOH group may be used singly or as
combinations of two or more thereof. The compound having a ≡C--COOH
group is added in an amount ranging from 0 to 5 parts, preferably 0.1 to
5 parts, more preferably 0.1 to 3 parts, and further preferably 0.1 to 2
parts by weight, per 100 parts by weight of the base polymer (B). Up to 5
phr of the compound may have a minimal risk of reducing the resolution of
the resist composition.

[0169]Preferred examples of the acetylene alcohol derivative which can be
added to the resist composition include those having the general formula
(S1) or (S2) below.

##STR00077##

In the formulas, R501, R502, R503, R504, and R505
are each hydrogen or a straight, branched or cyclic C1-C8
alkyl; and X and Y are each 0 or a positive number, satisfying
0≦X≦30, 0≦Y≦30, and 0≦X+Y≦40.

[0171]The acetylene alcohol derivative is preferably added in an amount of
0.01 to 2%, and more preferably 0.02 to 1% by weight based on the resist
composition. At least 0.01 wt % of the acetylene alcohol derivative is
effective for improving the coating characteristics and shelf stability
whereas up to 2 wt % may have little impact on the resolution of the
resist composition.

[0172]The resist composition of the invention may include optional
ingredients, for example, a surfactant which is commonly used for
improving the coating characteristics. Optional ingredients may be added
in conventional amounts so long as this does not compromise the objects
of the invention.

[0174]It is now described how to form a pattern using the resist
composition of the invention. A pattern may be formed from the resist
composition of the invention using any well-known lithography process.
The preferred method includes at least the steps of forming a photoresist
coating on a substrate, exposing it to high-energy radiation, and
developing it with a developer.

[0175]For example, the resist composition is applied onto a substrate,
typically a silicon wafer by a suitable coating technique such as spin
coating. The coating is prebaked on a hot plate at a temperature of 60 to
150° C. for 1 to 10 minutes, preferably 80 to 140° C. for 1
to 5 minutes, to form a resist film of 0.1 to 2.0 μm thick. It is
noted in conjunction with spin coating that if the resist composition is
coated onto the surface of a substrate which has been wetted with the
resist solvent or a solution miscible with the resist solvent, then the
amount of the resist composition dispensed can be reduced (see JP-A
9-246173).

[0176]A patterning mask having the desired pattern is then placed over the
photoresist film, and the film exposed through the mask to an electron
beam or to high-energy radiation such as deep-UV, excimer laser or x-ray
in a dose of 1 to 200 mJ/cm2, and preferably 10 to 100 mJ/cm2.
The high-energy radiation used herein preferably has a wavelength in the
range of 180 to 250 nm.

[0177]Light exposure may be dry exposure in air or nitrogen atmosphere, EB
or EUV exposure in vacuum, or immersion lithography of providing a
liquid, typically water between the photoresist film and the projection
lens.

[0178]The immersion lithography involves prebaking a resist film and
exposing the resist film to light through a projection lens, with
deionized water or similar liquid interposed between the resist film and
the projection lens. Since this allows projection lenses to be designed
to a NA of 1.0 or higher, formation of finer patterns is possible. The
immersion lithography is important for the ArF lithography to survive to
the 45-nm node. The liquid used herein may be a liquid with a refractive
index of at least 1 which is highly transparent at the exposure
wavelength, typically deionized water or alkane.

[0179]The photoresist film formed from the resist composition of the
invention has such barrier properties to water that it may inhibit resist
components from being leached out in water and as a consequence,
eliminate a need for a protective coating in immersion lithography and
reduce the cost associated with protective coating formation or the like.
The photoresist film has so high a receding contact angle with water that
few liquid droplets may be left on the surface of the photoresist film
after immersion lithography scanning, minimizing pattern formation
failures induced by liquid droplets left on the film surface.

[0180]In another version of immersion lithography, a protective coating
may be formed on top of the resist film. The resist protective coatings
generally include solvent-strippable type and developer-soluble type
coatings. A protective coating of the developer-soluble type is
advantageous for process simplification in that it can be stripped during
development of the photoresist film.

[0181]The resist protective coating used in the immersion lithography may
be formed from a coating solution, for example, a solution of a polymer
having acidic units such as 1,1,1,3,3,3-hexafluoro-2-propanol residues,
carboxyl or sulfo groups which is insoluble in water and soluble in an
alkaline developer liquid, in a solvent selected from alcohols of at
least 4 carbon atoms, ethers of 8 to 12 carbon atoms, and mixtures
thereof. The resist protective coating is not limited thereto.

[0182]The resist protective coating may be formed by spin coating a
topcoat solution onto a prebaked photoresist film, and prebaking on a hot
plate at 50 to 150° C. for 1 to 10 minutes, preferably at 70 to
140° C. for 1 to 5 minutes. Preferably the protective coating has
a thickness in the range of 10 to 500 nm. As in the case of resist
compositions, the amount of the protective coating material dispensed in
forming a protective coating by spin coating may be reduced by previously
wetting the resist film surface with a suitable solvent and applying the
protective coating material thereto.

[0183]After exposure to high-energy radiation through a photomask, the
resist film is post-exposure baked (PEB) on a hot plate at 60 to
150° C. for 1 to 5 minutes, and preferably at 80 to 140° C.
for 1 to 3 minutes.

[0184]Where a resist protective coating is used, sometimes water is left
on the protective coating prior to PEB. If PEB is performed in the
presence of residual water, water can penetrate through the protective
coating to suck up the acid in the resist during PEB, impeding pattern
formation. To fully remove the water on the protective coating prior to
PEB, the water on the protective coating should be dried or recovered by
suitable means, for example, spin drying, purging the protective coating
surface with dry air or nitrogen, or optimizing the shape of a water
recovery nozzle on the relevant stage or a water recovery process.

[0185]After exposure, development is carried out using as the developer an
aqueous alkaline solution, such as a 0.1 to 5 wt %, preferably 2 to 3 wt
%, aqueous solution of tetramethylammonium hydroxide (TMAH), this being
done by a conventional method such as dip, puddle, or spray development
for a period of 10 to 300 seconds, and preferably 0.5 to 2 minutes. A
typical developer is a 2.38 wt % TMAH aqueous solution. These steps
result in the formation of the desired pattern on the substrate.

[0186]Where polymer (A) is used as an additive to a resist material for
use with mask blanks, a resist solution is prepared by adding polymer (A)
to any one of the aforementioned base resins. The resist solution is
coated on a mask blank substrate of SiO2, Cr, CrO, CrN, MoSi or the
like. By further forming a SOG film and an organic undercoat film between
the photoresist and the blank substrate, there is provided a three-layer
structure which is also acceptable herein.

[0187]As the base resin of the resist composition for use with mask
blanks, novolac resins and hydroxystyrene are often used. Those resins in
which alkali soluble hydroxyl groups are substituted by acid labile
groups are used for positive resists while these resins in combination
with crosslinking agents are used for negative resists. Base polymers
which can be used herein include copolymers of hydroxystyrene with one or
more of (meth)acrylic derivatives, styrene, vinyl naphthalene, vinyl
anthracene, vinyl pyrene, hydroxyvinyl naphthalene, hydroxyvinyl
anthracene, indene, hydroxyindene, acenaphthylene, and norbornadiene.

[0188]Once the resist coating is formed, the structure is exposed to EB in
vacuum using an EB image-writing system. The exposure is followed by
post-exposure baking (PEB) and development in an alkaline developer for
10 to 300 seconds.

EXAMPLE

[0189]Examples of the invention are given below by way of illustration and
not by way of limitation. The abbreviations used herein are GPC for gel
permeation chromatography, NMR for nuclear magnetic resonance, Mw for
weight average molecular weight, Mn for number average molecular weight,
and Mw/Mn for molecular weight dispersity. Mw and Mn are determined by
GPC versus polystyrene standards.

Polymer Synthesis Example

[0190]Monomers 1 to 10 used in Polymer Synthesis Examples are identified
below by their structural formula.

##STR00078## ##STR00079##

Polymer Synthesis Example 1

[0191]Copolymerization of Monomers 1, 2 and 6 (40/30/30)

[0192]To a flask in a nitrogen blanket, 45.94 g of Monomer 1, 19.30 g of
Monomer 2, 35.55 g of Monomer 6, and 42.9 g of γ-butyrolactone were
fed to form a monomer solution, which was kept at a temperature of
20-25° C. With stirring, the solution was heated to 60° C.,
whereupon 4.51 g of dimethyl 2,2'-azobis(isobutyrate) was added. The
polymerization solution was continuously stirred for 24 hours while
keeping the temperature at 60° C. At the end of maturing, the
solution was cooled to room temperature. To the polymerization solution
thus obtained, 300 g of diisopropyl ether and 300 g of ultra-pure water
were added, followed by 15 minutes of stirring. The water layer was
discarded, and the organic layer was washed three times with 300 g of
water. The organic layer was concentrated and added dropwise to 1,500 g
of hexane. The precipitated copolymer was separated and washed twice with
600 g of hexane, whereupon white solids were isolated. The white solids
were vacuum dried at 50° C. for 24 hours, obtaining 53.6 g of the
target polymer, Polymer 1. The resin was analyzed for composition by
1H-NMR, finding that the copolymer consisted of Monomers 1, 2 and 6
in a ratio of 53/29/18 mol %. The copolymer was also analyzed for
molecular weight by GPC, finding Mw of 7,100 and Mw/Mn of 1.4.

Polymer Synthesis Examples 2 to 6

[0193]Like Polymer 1, Polymers 2 to 6 were synthesized in accordance with
the formulation shown in Table 1 and analyzed by GPC. The results are
shown in Table 1.

Copolymerization of Monomers 1 and 6 (70/30) and Post-Protection Reaction

[0194]To a flask in a nitrogen blanket, 73.28 g of Monomer 1, 30.42 g of
Monomer 6, and 42.9 g of γ-butyrolactone were fed to form a monomer
solution, which was kept at a temperature of 20-25° C. With
stirring, the solution was heated to 60° C., whereupon 3.47 g of
dimethyl 2,2'-azobis-(isobutyrate) was added. The polymerization solution
was continuously stirred for 24 hours while keeping the temperature at
60° C. At the end of maturing, the solution was cooled to room
temperature. To the polymerization solution thus obtained, 300 g of
diisopropyl ether and 300 g of ultra-pure water were added, followed by
15 minutes of stirring. The water layer was discarded, and the organic
layer was washed three times with 300 g of water. The organic layer was
concentrated and added dropwise to 1,500 g of hexane. The precipitated
copolymer was separated and washed twice with 600 g of hexane, whereupon
white solids were isolated. The white solids were vacuum dried at
50° C. for 24 hours, obtaining 50.6 g of the target polymer,
Polymer 7'. The resin was analyzed for composition by 1H-NMR,
finding that the copolymer consisted of Monomers 1 and 6 in a ratio of
72/28 mol %. The copolymer was also analyzed for molecular weight by GPC,
finding Mw of 9,000 and Mw/Mn of 1.4.

[0195]Next, in a nitrogen atmosphere, a 50 g portion of Polymer 7' was
dissolved in 200 g of tetrahydrofuran. With the flask in an ice bath, 4.6
g of triethylamine and 4.6 g of 1-chloro-1-methoxy-2-methylpropane were
added to the solution, which was continuously stirred for 10 hours at
room temperature. To the flask, 100 g of diisopropyl ether and 150 g of
water were added, followed by stirring. After the water layer was
separated off, the organic layer was concentrated. The concentrate was
added dropwise to 750 g of hexane. The precipitated copolymer was
separated and washed twice with 300 g of hexane, whereupon white solids
were isolated. The white solids were vacuum dried at 50° C. for 24
hours, obtaining 44.1 g of the target polymer, Polymer 7. The resin was
analyzed for percent protection of hydroxyl groups by 1H-NMR,
finding that 28% of overall hydroxyl groups had been substituted by
1-methoxy-2-methylpropyl groups. The copolymer was also analyzed for
molecular weight by GPC, finding Mw of 9,200 and Mw/Mn of 1.4.

##STR00086##

Comparative Polymer Synthesis Example 1

[0196]Synthesis of homopolymer of Monomer 9

[0197]To a flask in a nitrogen blanket, 100.0 g of Monomer 9, 3.91 g of
dimethyl 2,2'-azobis(isobutyrate), and 100.0 g of isopropyl alcohol were
fed to form a monomer solution, which was kept at a temperature of
20-25° C. To another flask in a nitrogen blanket, 50.0 g of
isopropyl alcohol was fed. With stirring, it was heated to 80° C.,
to which the monomer solution was added dropwise over 4 hours. After the
completion of dropwise addition, the polymerization solution was
continuously stirred for 3 hours while keeping the temperature at
80° C. After the maturing, the solution was cooled to room
temperature. The polymerization solution thus obtained was added dropwise
to 2,000 g of water, after which the precipitated polymer was filtered.
The polymer was washed four times with 600 g of a 9/1 solvent mixture of
hexane and isopropyl ether, whereupon white solids were isolated. The
white solids were vacuum dried at 50° C. for 20 hours, obtaining
92.8 g of the target polymer, Comparative Polymer 1. The polymer was
analyzed by GPC, finding Mw of 7,800 and Mw/Mn of 1.6.

Comparative Polymer Synthesis Example 2

[0198]Synthesis of homopolymer of Monomer 10

[0199]A homopolymer of Monomer 10 was synthesized in accordance with the
same formulation as in Comparative Polymer Synthesis Example 1. The
polymer, Comparative Polymer 2, was analyzed by GPC, finding Mw of 7,900
and Mw/Mn of 1.6.

Evaluation of Resist Coating

[0200]Resist solutions were prepared by dissolving 5 g of Resist Polymer
(shown below), 0.5 g of an additive polymer selected from Polymers 1 to 7
and Comparative Polymers 1 and 2, 0.25 g of PAG1, and 0.05 g of Quencher
1 in 75 g of propylene glycol monoethyl ether acetate (PGMEA), and
filtering through a polypropylene filter having a pore size of 0.2 μm.
A control resist solution was similarly prepared without adding the
additive polymer.

##STR00087##

[0201]An antireflective coating ARC-29A (Nissan Chemical Co., Ltd.) of 87
nm thick was formed on a silicon substrate, after which each resist
solution was applied onto the ARC and baked at 120° C. for 60
seconds to form a resist film of 150 nm thick.

[0202]A contact angle with water of the resist film was measured, using an
inclination contact angle meter Drop Master 500 by Kyowa Interface
Science Co., Ltd. Specifically, the wafer covered with the resist film
was kept horizontal, and 50 μL of pure water was dropped on the resist
film to form a droplet. While the wafer was gradually inclined, the angle
(sliding angle) at which the droplet started sliding down was determined
as well as receding contact angle. The results are shown in Table 2.

[0203]A smaller sliding angle indicates an easier flow of water on the
resist film. A larger receding contact angle indicates that fewer liquid
droplets are left during high-speed scan exposure. It is demonstrated in
Table 2 that the inclusion of the additive polymer of the invention in a
resist solution achieves a drastic improvement in the receding contact
angle of photoresist film without adversely affecting the sliding angle,
as compared with the comparative photoresist films containing comparative
additive polymers and the control photoresist film.

[0204]Also, the resist film-bearing wafer (prepared above) was irradiated
through an open frame at an energy dose of 50 mJ/cm2 using an ArF
scanner S305B (Nikon Corp.). Then a true circle ring of Teflon®
having an inner diameter of 10 cm was placed on the resist film, 10 mL of
deionized water was carefully injected inside the ring, and the resist
film was kept in contact with water at room temperature for 60 seconds.
Thereafter, the water was recovered, and a concentration of photoacid
generator (PAG1) anion in the water was measured by an LC-MS analyzer
(Agilent). The anion concentration measured indicates an amount of anions
leached out for 60 seconds. The results are shown in Table 2.

[0205]As is evident from Table 2, the photoresist films formed from the
resist solutions having the additive polymers of the invention compounded
therein are effective for preventing the PAG component from being leached
out in water.

[0206]Further, the resist film-bearing wafer (prepared above) was exposed
by means of an ArF scanner model S307E (Nikon Corp., NA 0.85, σ
0.93, 4/5 annular illumination, 6% halftone phase shift mask), rinsed for
5 minutes while splashing deionized water, post-exposure baked (PEB) at
110° C. for 60 seconds, and developed with a 2.38 wt % TMAH
aqueous solution for 60 seconds, forming a 75-nm line-and-space pattern.
The wafer was sectioned, and the profile and sensitivity of the 75-nm
line-and-space pattern were evaluated. The results are also shown in
Table 2.

[0207]It is seen from Table 2 that when exposure is followed by water
rinsing, the resist film having the additive polymer of the invention
formulated therein formed a pattern of rectangular profile, in stark
contrast with the control resist film free of the additive polymer
forming a pattern of T-top profile.

[0209]Although some preferred embodiments have been described, many
modifications and variations may be made thereto in light of the above
teachings. It is therefore to be understood that the invention may be
practiced otherwise than as specifically described without departing from
the scope of the appended claims.